Localisation and expression of aquaporin-4 around arterioles, venules and capillaries in the rat spinal cord

The traditional view of cerebrospinal fluid (CSF) circulation within the central nervous system (CNS) is that CSF is produced within the choroid plexus, flows slowly through the subarachnoid space (SAS). and is reabsorbed by arachnoid villi or around spinal nerves. Despite acceptance of this viewpoint, the mechanism by which CSF is moved around the CNS is not fully understood. Our current understanding of CSF flow within the brain is that fluid inflow occurs predominantly around peri-arterial spaces, whilst outflow occurs around peri-venular spaces. This fluid movement is believed to be mediated by the protein aquaporin-4 (AQP4). Whether AQP4 contributes to the movement of CSF within the spinal cord remains to be determined. The aim of the following study was to assess AQP4 expression in the rodent spinal cord in relation to microvascular structures. Multiple labelling immunohistochemistry was performed on 6 and 12 week old rats to distinguish arterioles from venules, and capillaries were identified by measuring the diameter of each stained vessel. AQP4 was found around both arterioles and venules within the rodent spinal cord, and was expressed in higher levels in the younger rats. No overall difference was found between AQP4 expression levels around arterioles, venules and capillaries, however, expression of AQP4 was found to decrease as the diameter of arterioles increased. The results of this study lay the foundation for future experiments to assess the effect of AQP4 antagonism on fluid flow within the spinal cord.